This application is based on and claims the priority under 35 U.S.C. xc2xa7119 of German Patent Application 199 56 675.5, filed on Nov. 25, 1999, the entire disclosure of which is incorporated herein by reference.
The invention relates to a plastic housing for receiving an assembly of electric and electronic components mounted on a circuit board, particularly providing protection against condensation of moisture on the electric and electronic components.
It has previously been typical to enclose electric and electronic components mounted on circuit boards within metal housings for protecting the electric and electronic assemblies from external damage, environmental elements, etc. It is recently becoming common to provide synthetic plastic housings instead of the metal housings for enclosing such electric and electronic assemblies, especially in the field of electrical and electronic systems for motor vehicles, in view of the reduced weight, reduced cost, and advantageous production methods for the plastic housings in comparison to the metal housings.
While such plastic housings are typically protected against direct entry of water sprays or the like, they are often not hermetically tightly sealed, so that humidity or moisture in the air can penetrate into the interior of such plastic housings. This leads to the disadvantage, that a reduction in the environmental mental temperature can cause the humidity or moisture in the air within the housing to condense therein. In this context, the moisture predominantly or preferentially condenses on any metal surfaces within the housing, because such metal surfaces have a higher thermal conductivity and a more-rapid temperature variation response than the plastic material of the plastic housing itself. Thus, the condensate often forms predominantly on the electric and electronic components of the assembly within the housing, rather than on the interior wall surface of the plastic housing itself. In comparison, such condensate within a metal housing would typically condense on the surfaces of the metal housing itself, where it would not be dangerous or damaging to the electric and electronic components.
In order that the moisture condensing on the electric and electronic components does not lead to short-circuiting, current leakage or corrosion of the electric and electronic assemblies, in many cases the electric and electronic components are sealed with a protective lacquer, resin layer, or other encapsulants. Such protective measures, however, cause the disadvantage that the electric and electronic components are no longer accessible in order to test the components, update or maintain software, monitor the long-term behavior thereof, or the like. For this reason, it often becomes necessary to exchange the entire electric or electronic assembly such as a control device, rather than simply exchanging individual components thereof, which thus leads to higher maintenance and repair costs.
In view of the above, it is an object of the invention to provide a housing for receiving electric and electronic assemblies, wherein the housing is predominantly made of plastic and includes structural measures to help avoid the condensation of humidity or moisture onto the electric and electronic components enclosed within the housing in the event of temperature variations. The invention also aims to avoid the need for providing protective seal layers for encapsulating the electric and electronic components within such a housing. It is a further aim of the invention to avoid the disadvantages of the prior art, and to achieve additional advantages, as apparent from the present specification.
The above objects have been achieved according to the invention in an arrangement comprising a housing for receiving electric and electronic assemblies including electric and electronic components mounted on a circuit board. According to the invention, the housing includes a housing floor as well as a housing lid or cover, whereby at least the cover is made of plastic. Furthermore, a metal component with at least one surfacially extending metal surface is arranged within the housing in order to preferentially condense moisture such as air humidity on this metal surface. For example, the metal component including the metal surface may comprise a metal casing or enclosure provided around at least one of the electric or electronic components, or a metallizing layer provided on the inner surface of the plastic housing itself, or a metal insert member that is inserted into or onto the plastic housing, or an additional metal floor plate arranged adjacent to or along the housing floor, or the housing floor itself may be a metal component.
When a temperature change leads to condensation of any humidity or other moisture within the housing, the condensation will predominantly or preferentially occur on the metal surface provided for this purpose within the housing. Thus, the condensation will not occur directly on the electric or electronic components, and it becomes unnecessary to provide a protective encapsulating layer on the electric and electronic components. Further according to the invention, condensate drain holes and additional means may be provided to channel and drain away any condensate that forms.
In this manner, according to the invention, the dangers of short-circuiting, circuiting, leakage currents, and corrosion can be avoided. Also, the electric and electronic components within the housing remain freely accessible for testing and maintenance purposes, so that any necessary changes can be carried out. Also, for recycling the overall housing-enclosed assembly, it is a simple matter to separate the metal parts and the plastic parts for separately recycling these respective parts. The invention is especially suitable for use in plastic housings enclosing electric and electronic components, such as those typically included in control devices provided in motor vehicles.